(a) Field of the Invention
The present invention relates to a battery module and, more particularly, to the structure of a module battery including a flat secondary battery.
(b) Description of the Related Art
It is generally known that a secondary battery has a drawback in that the iterative charge and discharge operation causes generation of internal gas, which enters between electrodes of the battery cell to degrade the performance of the secondary battery. In particular, a secondary battery cell having a laminate overcoat suffers from a volume increase within the overcoat due to the internal gas to enlarge the gap between the electrodes of a battery body, thereby largely degrading the performance of the secondary battery.
For solving the above problem in a battery module including a battery cell having a laminate overcoat, an electrolytic solution having a function for suppressing the gas generation and/or a cell structure configured to suppress the increase of the electrode gap of the battery cell is generally employed. However, such an electrolytic solution does not in fact effectively prevent the volume increase due to the gas generation during the long lifetime of the secondary battery. In addition, the structure configured to suppress the increase of the electrode gap increases the weight per unit cell, thereby reducing the current storage capacity per unit weight of the secondary battery or a module including a plurality of such secondary batteries.